ViraCore is a biotechnology company developing a drug discovery tool, the cell-array, that enables scientists in academia and industry to determine the function of thousands of protein variants simultaneously without the need for prior sequencing or individual site-directed mutagenesis. We propose here to produce and use a cell-array that is capable of simultaneously expressing thousands of arrayed HIV Envelope (Env) proteins within living cells on a 1x3 inch glass slide. Each of the thousands of Env proteins will contain discrete, defined mutations that can enable antigenic and functional characterization of the protein. Importantly, each of the thousands of proteins is expressed in a living cell, thus preserving the structure and function of this highly complex, oligomeric molecule. We expect that Phase I will enable us to further develop and validate the tools required to build cell-arrays for studying Env. In Phase II, we will use the mutant Env arrays to screen for Env mutants that can serve as better immunogens, that expose hidden epitopes, that retain structural integrity after exposure to adverse conditions, that alter their requirements for receptor/coreceptor activation, and that have altered processing. PROPOSED COMMERCIAL APPLICATION: The application of HIV mutation libraries with cell-arrays contributes to basic and clinical tools for HIV research. HIV research amounted to one of the largest single scientific categories of last year's $20 billion expenditures on basic research. For clinical applications, Env arrays are expected to be most useful for vaccine trials. Cell-arrays focused on other HIV genes (e.g. Pol) are likely to be most useful for commercial development of HIV therapeutics and for the detection of multi-drug resistant viruses.